Abstract 15869: PDZK1 Prevents Neointima Formation via Suppression of Breakpoint Cluster Region Kinase Function in Vascular Smooth Muscle
In endothelial cells, kinase activation by the HDL receptor scavenger receptor class B, type I (SR-BI) stimulates endothelial NO synthase and cell migration. These processes require the C-terminal PDZ-interacting domain of SR-BI and the PDZ domain-containing adaptor protein PDZK1. Whether SR-BI and/or PDZK1 are operative in vascular smooth muscle (VSM) is unknown. Both SR-BI and PDZK1 proteins were detected by immunoblot analysis in primary murine VSM cells and stable VSM cell lines. To determine the impact of SR-BI and PDZK1 on VSM behavior in vivo, neointima formation was assessed 14 days post-ligation in the carotid arteries of wild-type, SR-BI-/- or PDZK1-/- mice. Neointima development was negligible in wild-type and SR-BI-/- mice. In contrast, although lipoprotein profiles are similar in SR-BI-/- and PDZK1-/- due to comparable loss of hepatic SR-BI, there was marked neointima formation in PDZK1-/- mice. In addition, compared to primary VSM cells from PDZK1+/+ mice, PDZK1-/- VSM cells displayed exaggerated migration and proliferation in response to PDGF. By tandem affinity purification and mass spectrometry it was determined that PDZK1 interacts with breakpoint cluster region kinase (Bcr), which contains a C-terminal PDZ binding sequence and is known to promote PDGF signaling in VSM. Coimmunoprecipitation studies in primary murine VSM cells confirmed PDZK1 interaction with Bcr, and whereas the overexpression of wild-type Bcr in murine VSM cells caused no change in PDGF-induced cell proliferation, the overexpression of a mutant form of Bcr incapable of PDZK1 binding resulted in exaggerated proliferation. Moreover, the enhanced growth observed in PDZK1-/- VSM cells was abrogated by siRNA-based depletion of Bcr. Thus, PDZK1 has novel SR-BI-independent function that affords protection from neointima formation, and in VSM PDZK1 tempers PDGF-induced VSM proliferation via its interaction with Bcr and associated suppression of Bcr function. Independent of plasma lipoproteins and SR-BI, PDZK1 now warrants consideration as a gene relevant to the risk of vascular disorders involving neointima formation and restenosis. In addition, these processes can potentially be harnessed to regulate VSM growth or migration.
- © 2013 by American Heart Association, Inc.